CN103977689B - Device and method for removing sulfur dioxide in smoke by two-step alkalifying reproducing and sodium sulfite method - Google Patents

Abstract

The invention discloses a device and method for removing sulfur dioxide in smoke by the two-step alkalifying reproducing and sodium sulfite method, and aims at overcoming the shortages of an existing sodium-sulfite-method desulfurization technology. The method is characterized in that a reproducing unit performs reproduction in two steps; an absorbing unit is used for absorbing sulfur dioxide from the smoke twice with absorbing solutions composed of different components, wherein in the first reproduction step, most of sodium hydrogen sulfite is removed to obtain a sodium sulfite crystal, and in the second reproduction step, all sodium hydrogen sulfite is removed to obtain a pure sodium sulfite solution with high absorbing capacity; the mixing solution of sodium sulfite and sodium hydrogen sulfite is used to absorb in a main absorbing stage; in a fine absorbing stage, the pure solution, with high absorbing capability, which is obtained by reproducing is used to continuously desulfurize the smoke desulfurized in the main absorbing stage so that the content of sulfur dioxide in the clean smoke is reduced to be less than 40mg/m<3>. According to the device and method, the balance among the investment, desulfurization degree, operation economy and reliability is ensured, so that compared with a calcium-method desulfurization technology and a ammonia-method desulfurization technology, the method according to the invention has the advantage that the lower cost and higher desulfurization degree can be realized; the device and the method can be widely applied to thermal power plants, metallurgy, building materials and industrial furnaces.

Description

Device and method for removing sulfur dioxide from flue gas by adding alkali and regenerating sodium sulfite in two steps

technical field

The invention relates to industries such as chemical industry, thermoelectricity, metallurgy and building materials, and in particular relates to a device and method for removing sulfur dioxide from flue gas by two-step alkali addition and regeneration of sodium sulfite.

Background technique

Principles of various existing flue gas desulfurization technologies:

Sodium sulfite method

Sodium sulfite absorption desulfurization technology is divided into two types of processes: heating regeneration and alkali addition regeneration according to the regeneration method of absorbing rich liquid. The heating regeneration process obtains sulfur dioxide gas during absorption of rich liquid regeneration, which can be further processed into sulfuric acid, sulfur or other products with higher value. It has the disadvantages of complicated process and high regeneration energy consumption, and is only suitable for comprehensive utilization of large-scale flue gas desulfurization project.

The currently operating sodium sulfite desulfurization device has a simple process and low energy consumption, but generally uses 400 mg/ ^m3 as the tail gas control index, which obviously cannot meet the boiler flue gas emission standard and cannot be promoted in the field of boiler flue gas desulfurization.

The principle and process of alkali regeneration sodium nitrite desulfurization technology:

No matter it is the sodium sulfite desulfurization technology of caustic soda or soda ash to regenerate and absorb the rich liquid, the circulating absorption liquid is a mixed solution of sodium sulfite and sodium bisulfite, and the desulfurization system is divided into an absorption unit and a regeneration unit.

The absorption unit refers to the reaction unit in which the mixed solution of sodium sulfite and sodium bisulfite reacts with the flue gas containing SO ₂ to absorb SO ₂ . The reaction process is carried out in the spray tower. The droplet of the mixed solution is in full contact with the flue gas. The Na ₂ SO ₃ in the droplet reacts with the SO ₂ in the flue gas to form NaHSO ₃ :

Na ₂ SO ₃ + SO ₂ + H ₂ O = 2NaHSO ₃

In the above reactions, the greater the concentration of Na ₂ SO ₃ in the liquid phase, the lower the equilibrium SO ₂ concentration in the gas phase, and the greater the driving force for SO ₂ absorption. The greater the concentration of the reaction product NaHSO ₃ in the liquid phase, the higher the concentration of SO ₂ in the gas phase equilibrium, and the smaller the driving force for SO ₂ absorption.

The longer the gas-liquid contact time, the larger the exchange area and the higher the absorption degree. The gas-liquid contact time is mainly determined by the height of the contact area of the absorption tower and the flow rate of the flue gas, and the exchange area is determined by the amount of absorbed liquid and the average particle size of the droplets.

The regeneration unit refers to the unit that adds alkali to the absorption rich liquid to restore the absorption capacity of the absorption rich liquid. Its function is to first adjust the pH value of the absorption liquid to maintain the absorption capacity of the circulating absorption liquid, and secondly separate the excess sulfite in the absorption liquid to maintain the material balance of the absorption liquid. The essence of adjusting the pH value of the absorption liquid is to convert NaHSO ₃ generated by absorbing sulfur dioxide in the absorption liquid into Na ₂ SO ₃ .

The regeneration unit first regenerates the absorption liquid with the following reactions:

Caustic soda regeneration: NaHSO ₃ +NaOH=Na ₂ SO ₃ +H ₂ O

Regeneration of soda ash: 2NaHSO ₃ +Na ₂ CO ₃ =2Na ₂ SO ₃ +H ₂ O+CO ₂ ↑

The original sodium sulfite desulfurization technology has a low concentration of the absorption liquid, and the solution after reacting with caustic soda needs to undergo forced circulation evaporation to supersaturate sodium sulfite to produce partial crystallization, and then separate the crystallization from the solution by filtration, and the separated crystallization is washed and dried Dry to obtain the by-product sodium sulfite product. After filtering and separating sodium sulfite crystallization, the mother liquor composition is mainly sodium sulfite and contains a large amount of sodium bisulfite, but the pH value of the mother liquor is higher than the circulating absorption liquid of the absorption system, and returning the mother liquor to the circulating absorption liquid of the absorption system can maintain the pH value of the absorption liquid, Restores its ability to continue absorbing. Generally control the pH value of the circulating absorption solution to 6.5-7.5.

Later improved sodium sulfite desulfurization technology, the difference in the regeneration process of the absorption liquid is that, because the concentration of the absorption liquid controlled by the absorption unit is relatively high, the solubility of the product sodium sulfite is lower than that of sodium bisulfite in the regeneration unit. After that, sodium sulfite crystals are formed in the solution.

A large amount of carbon dioxide gas is produced in the regeneration reaction of soda ash, and the gas generates foam in the reactor, and corresponding defoaming measures should be taken. In order to prevent the unreacted soda ash from entering the absorption unit with the mother liquor to produce foam when the soda ash is excessive, and to take advantage of the characteristic that the solubility of sodium bisulfite is higher than that of sodium sulfite, the pH value of the absorption liquid controlled by the absorption unit is lower than the pH index of caustic soda regeneration. At pH 5.8-6.5. Among them, the pH value of the solution after the regeneration reaction of the neutralization unit is also relatively low, that is, the regeneration of the absorption liquid cannot be fully in place, so that the decomposition of sodium bisulfite is not complete.

Principle and process of calcium desulfurization technology

Reaction of limestone with sulfur dioxide in the presence of water:

CaCO ₃ +SO ₂ +1/2H ₂ O = CaSO ₃ 1/2H ₂ O↓ +CO ₂ ↑

The product calcium sulfite is unstable and can react with oxygen:

CaSO ₃ 1/2H ₂ O+1/2O ₂ +(1+1/2)H ₂ O= CaSO ₄ 2H ₂ O↓

The limestone/lime-gypsum flue gas desulfurization technology device consists of an absorbent preparation system, an absorption and oxidation system, a desulfurization by-product treatment system, and a desulfurization wastewater treatment system. Limestone is used as a desulfurizer. Limestone is crushed and ground into powder and mixed with water to make absorption slurry. When lime is used as absorbent, lime powder is digested and then stirred with water to make absorption slurry. In the absorption tower, the absorption slurry is contacted and mixed with the flue gas. The sulfur dioxide in the flue gas reacts with the calcium hydroxide in the slurry and the blown air, and the final reaction product is gypsum. The desulfurized flue gas passes through the demister to remove the fine liquid droplets, and is discharged into the chimney after being heated by the heat exchanger. The by-product gypsum produced by desulfurization is not of high utilization value because it contains a large amount of impurities, and most of it is discarded after filtration and dehydration, resulting in secondary pollution.

Ammonia desulfurization technology principle and process

The main component of the circulating absorption liquid of the ammonia desulfurization technology is a mixed solution of ammonium bisulfite (NH ₄ HSO _{3 )} and ammonium sulfite ((NH ₄ ) ₂ SO ₃ ), and it is the mixture of ammonium sulfite and SO ₂ that works. chemical reaction:

(NH ₄ ) ₂ SO ₃ +SO ₂ +H ₂ O = 2NH ₄ HSO ₃

The reaction is carried out in an absorption tower with empty tower spraying. As the reaction continues to produce ammonium bisulfite, it is necessary to continuously add ammonia to the circulating absorption liquid to react with it to convert it into ammonium sulfite, thereby restoring the absorption capacity of the circulating absorption liquid and promoting the reaction to continue.

Ammonium bisulfite reacts with added ammonia:

NH ₄ HSO ₃ +NH ₃ = (NH ₄ ) ₂ SO ₃

At the same time of the above reaction, a large amount of air is blown into the circulation tank of the absorption tower to carry out the oxidation reaction with the circulating absorption liquid, so that the ammonium sulfite is converted into relatively stable ammonium sulfate, and the sulfur dioxide is truly stabilized in the solution. Oxidation reaction:

(NH ₄ )xH ₂ -xSO ₃ +1/2O ₂ +(2-x)NH ₃ =(NH ₄ ) ₂ SO ₄

The main process of ammonia desulfurization technology:

1. The flue gas contacts and reacts with ammonia water in the absorption tower, and _SO2 is absorbed to form ammonium sulfite, which is dissolved in the circulating absorption liquid, and the net flue gas after desulfurization is directly discharged into the atmosphere.

2. The solution containing ammonium sulfite is oxidized by air to become ammonium sulfate solution. With the continuous accumulation of absorption-oxidation-absorption, ammonium sulfate reaches a certain concentration.

3. The ammonium sulfate solution becomes supersaturated by evaporation and concentration, and the ammonium sulfate crystallizes.

4. The slurry containing ammonium sulfate crystals is centrifuged to obtain solid ammonium sulfate.

Advantages and disadvantages of existing technology

Calcium desulfurization technology

Due to the deposition or crystallization of Ca(OH) ₂ or CaCO ₃ in the raw material, and the crystallization of the reaction products CaSO ₃ and CaSO ₄ , the biggest difficulty in calcium desulfurization is the fouling and blockage of the absorption tower. In order to solve this problem, the limestone-lime method has been replaced by the limestone-gypsum method. That is, a large amount of compressed air is blown into the bottom of the circulation tank more than ten meters deep under the absorption tower to oxidize CaSO ₃ to CaSO ₄ (gypsum), which greatly reduces the chance of fouling and blockage in the tower. And the blown gas makes the feed liquid more uniform, and the desulfurization rate is also improved. Limestone, the raw material of the calcium method, has a wide range of sources and low prices, but the generated gypsum is used as building materials in a small amount and most of it is discarded. The biggest disadvantage of the calcium method desulfurization technology is that it absorbs a huge amount of slurry circulation and consumes a _lot of power, which makes the desulfurization cost the highest among all methods. The component content is low. To reduce the sulfur dioxide content in the net flue gas and improve the desulfurization rate, the only way to further increase the amount of circulating absorption liquid is. In this way, not only the power consumption of the circulating pump is doubled, but also the airflow resistance of the tower system will be greater, and the energy consumption of flue gas transportation will also be higher. If the flue gas desulfurization of high-sulfur coal is to meet the minimum emission requirements, the calcium method is even more powerless. Moreover, the amount of wastewater discharged is large and the treatment cost is high.

The complex management and operation of the whole system of the calcium method and the large initial investment are also important shortcomings.

The biggest advantage of the calcium desulfurization method is that the technology is very mature and has a high availability rate, especially for large-scale installations where the calcium method is almost dominating the world. The reason is that the practice period is long, and the experience accumulated in all aspects of research, design, construction and operation is rich.

Ammonia desulfurization technology

The by-product of ammonia desulfurization technology is ammonium sulfate product with high added value, which can partially offset the operating cost of the device. As the sulfur dioxide content in the flue gas increases, the operating cost advantage is more prominent compared with the calcium method.

Ammonia has high reactivity, and the liquid-gas ratio of the absorption tower is greatly reduced compared with the calcium method technology, so that the power consumption of the circulating pump is reduced by about 2/3 compared with the calcium method. The resistance of the desulfurization tower system is about 1200Pa, and the power consumption of flue gas is also significantly lower than that of the calcium method.

The desulfurizer and product of ammonia desulfurization are easily soluble substances, the circulating fluid has no fouling, and the wear is small, but the absorption liquid is acidic, and the requirements for equipment anti-corrosion are higher than those of calcium and sodium-alkali methods.

The ammonia desulfurization unit does not require a raw material pretreatment process, the treatment process of by-products is relatively simple, and the device occupies a small area, which is convenient for the transformation of old boilers.

The main problem with the ammonia method is that the contradiction between the desulfurization rate and the escape of ammonia cannot be reconciled, which is determined by the partial pressure of the gas phase of the ammonia solution. To improve the desulfurization rate, the absorption liquid with strong absorption capacity must have a higher pH value, resulting in more ammonia escape. Many ammonia desulfurization devices therefore have obvious aerosol phenomena that cannot be solved. The desulfurization rate of the existing ammonia technology can reach 95%. With the high-efficiency demisting device, the ammonia loss of the system is about 0.15%, which is generally higher.

Sodium sulfite method

Sodium sulfite desulfurization converts SO2 in the flue gas into sodium sulfite products with higher added value, which can offset most of the operating costs of the device. As the sulfur content of the flue gas increases, the operating cost advantage becomes more prominent.

Sodium sulfite has high solubility and strong absorption capacity. Compared with the calcium method, the liquid-gas ratio is greatly reduced and lower than that of the ammonia method. The power consumption of the circulating pump is about 3/4 lower than that of the calcium method for desulfurization. The resistance of the desulfurization tower system is about 1200Pa, and the power consumption of flue gas is also significantly lower than that of the calcium method.

The by-products of sodium sulfite desulfurization are highly stable without oxidation, which saves equipment and energy consumption for oxidizing air compression compared with calcium and ammonia methods.

The raw materials and products of sodium sulfite desulfurization are intrinsically safe.

The desulfurizing agent and product of sodium sulfite desulfurization are easily soluble substances. The circulating absorption liquid has no scaling and little wear. The absorption liquid is neutral to alkaline and less corrosive, and the amount of daily maintenance is small.

The main problem in the existing sodium sulfite desulfurization technology: the desulfurization rate of the existing technology is slightly higher than 90%, and there is still a lot of room for improvement. If the existing technology can be scientifically improved, the desulfurization rate can reach 99%.

The regeneration liquid returned to the absorption tower by the sodium sulfite method has a lower "gas phase sulfur dioxide equilibrium concentration" than the absorption liquid by the calcium method and ammonia method, which is the technical basis for achieving a higher desulfurization rate than the existing flue gas desulfurization technology. Making good use of this basic condition can achieve lower cost and higher desulfurization rate than calcium and ammonia desulfurization technologies.

Contents of the invention

The purpose of the present invention is to provide a simple structure, low investment, low energy consumption, high desulfurization rate, economical and reliable operation of the two-step alkali-added regenerated sodium sulfite and sulfur dioxide removal device in flue gas.

Another object of the present invention is to provide a method for removing sulfur dioxide in flue gas.

In order to overcome the deficiencies in the prior art, the technical solution of the present invention is solved like this: a kind of two-step alkali-adding regeneration sodium sulfite and sulfur dioxide removal device in flue gas, this device is made up of filter press, washing pump, chimney, absorption tower, Washing tower, washing liquid tank, first regenerator, first mixer, main absorption pump, feed pump, thickener, centrifuge, mother liquor tank, mother liquor pump, second regenerator, second mixer, fine absorption Composed of a pump and a filter feed pump, the special feature of the present invention is that the device includes a two-stage countercurrent absorption unit and a two-step alkali regeneration unit for the absorption liquid, wherein the two-stage countercurrent absorption unit consists of a chimney, an absorption tower, a washing tower , washing liquid tank, washing pump, filter press, main absorption pump, fine absorption pump and filter feed pump; the two-step alkali regeneration unit for the absorption liquid consists of a first regenerator, a first mixer, and a feed pump , thickener, centrifuge, mother liquor tank, mother liquor pump, second regenerator and second mixer; the flue gas pipe from outside the device is connected to the flue gas inlet at the lower part of the scrubber, and the scrubber is connected to the absorption at its upper part The flue gas channels of the towers are connected, the top outlet of the absorption tower is connected with the chimney; the washing tower is connected with the washing liquid tank below, the inlet of the washing pump is connected with the liquid outlet of the washing liquid tank through pipes, and the outlet is connected with the spraying of the washing tower through pipes The inlet of the filter feed pump is connected to the mud outlet at the bottom of the washing liquid tank through a valve, the outlet of the filter feed pump is connected to the liquid inlet of the filter press, and the discharge port of the filter press is connected to the side inlet of the washing liquid tank; The inlet of the absorption pump is connected to the liquid discharge port at the lower part of the absorption tower, and its outlet is connected to the spray nozzle on the side of the middle of the absorption tower; the inlet of the fine absorption pump is connected to the outlet of the second regenerator, and the outlet of the fine absorption pump passes through pipes and channels The valve is connected to the absorption liquid inlet on the upper side of the absorption tower; the liquid inlet of the first regenerator is connected to the outlet of the first mixer, the liquid outlet is connected to the inlet of the feed pump, and the exhaust gas at the top of the first regenerator The mouth is connected to the top of the washing tower through a pipeline, and the top inlet of the first mixer is used for adding alkali. The side outlet is connected to the inlet pipeline of the main absorption pump through a pipeline; One side overflow port is connected to the inlet of the mother liquor tank, and the bottom outlet of the thickener is connected to the centrifuge through pipes and valves; the inlet of the mother liquor pump is connected to the outlet of the mother liquor tank, and its outlet is connected to the side inlet of the second mixer through a valve. The top inlet of the second mixer is used for adding alkali and tap water, the bottom outlet is connected with the second regenerator inlet, and the second regenerator outlet is connected with the inlet of the fine absorption pump.

A kind of method for removing sulfur dioxide in the flue gas is carried out according to the following steps:

1) The flue gas containing sulfur dioxide and soot from outside the device enters the washing tower and contacts with the spray washing liquid from the washing pump to wash dust and cool down, and then enters the absorption tower from the bottom at a temperature of 55-65 ° C to flow upwards, and in the absorption tower The internal space is in full contact with the circulating absorption liquid sent by the main absorption pump and the regeneration absorption liquid fed by the fine absorption pump in turn, the sulfur dioxide in the flue gas reacts with the sodium sulfite in the circulation absorption liquid and the regeneration absorption liquid to form sodium bisulfite and The net flue gas after removing sulfur dioxide enters the chimney from the top of the absorption tower to be vented;

2) The washing liquid sprayed by the washing tower is mainly water, which contains smoke and a small amount of soluble salts brought in by the flue gas. After washing, the washing liquid is returned from the washing tower to the washing liquid tank, and the washed dust settles and accumulates at the bottom of the washing liquid tank, and is regularly sent to the filter press through the filter feeding pump to remove the dust in the washing liquid, and the separated The clear liquid is returned to the washing tank for recycling, and the dust sludge with a water content of 30-50% discharged from the filter press is transported outside and mixed with the slag, a small amount of soluble salts are brought out with the dust sludge, and the evaporated water of the washing liquid is replenished by tap water;

3) In the absorption tower, the flue gas and the absorption liquid undergo absorption reaction at 55°C-65°C and a gauge pressure of 3kPa. The absorption liquid sprayed in the middle is a mixed solution of sodium sulfite and sodium bisulfite, which is transported by the main absorption pump Circular absorption, the absorption liquid will consume part of the sodium sulfite to generate more sodium bisulfite during each cycle of the chemical reaction with the sulfur dioxide in the flue gas, and the outlet of the absorption tower will be diverted to a part of the absorption liquid in the regeneration unit. Sodium bisulfate and sodium sulfite brought back to the absorption tower are used to maintain the stable composition of the circulating absorption liquid, the pH value of the circulating absorption liquid is in the range of 5.8-6.5, and the concentration of gaseous sulfur dioxide in equilibrium with the liquid phase is 100-200 mg/m ³ ;

4) The absorption liquid used in the fine absorption section of the upper space of the absorption tower is the regenerated absorption liquid returned by the regeneration unit, its composition is close to pure sodium sulfite saturated solution, only contains a very small amount of sodium bisulfite, and its pH value is in the range of 10.0-10.8 , the gaseous sulfur dioxide concentration in equilibrium with the liquid phase is 6-10 mg/m ³ ;

5) The fine absorption section on the upper part of the absorption tower is a packing and tray structure, all the regenerated absorption liquid passes through the packing layer at one time and no longer circulates, the pH value of the absorption liquid flowing down from the packing layer is in the range of 9-10, and it is replenished into the middle of the absorption tower The circulating absorption liquid keeps the pH value of the circulating absorption liquid in the main absorption section stable in the range of 5.8-6.5;

6) By sending a part of the absorption liquid to the regeneration unit for regeneration by adding alkali to maintain the pH value of the circulating absorption liquid in the absorption tower in the range of 5.8-6.5 to maintain its continuous desulfurization ability, the regeneration by adding alkali can use caustic soda or With soda ash, a part of the circulating absorption liquid discharged from the liquid collection section at the lower part of the absorption tower is split into the first regenerator through the first mixer for regeneration reaction. The amount of split depends on the amount of sulfur dioxide brought in by the flue gas. Sodium becomes sodium sulfite with lower solubility, part of sodium sulfite crystallizes in the first regenerator, more sodium sulfite dissolves in mother liquor and is separated by centrifuge and then enters mother liquor tank, sodium sulfite crystals separated by centrifuge are discharged into the finished product The equipment is dried and packaged for storage, and the centrifuged sodium sulfite crystals leave the solution system to maintain the material balance of the circulating absorption solution;

7) There is a small amount of undecomposed sodium bisulfite in the mother liquor after the separation of sodium sulfite crystals. The mother liquor is transported by the mother liquor pump through the second mixer and enters the second regenerator for further regeneration reaction so that all sodium bisulfite is converted into sodium sulfite. The second The regenerator also adds metered tap water to maintain the water balance of the absorption tower, that is, the water content of the circulating absorption liquid is within a controllable range, and solid crystallization does not occur in the absorption tower during the absorption process and can be produced in the reaction of the first regenerator. Sodium sulfite crystals;

8) The amount of water added to the washing tower is controlled by the liquid level of the washing liquid tank, the amount of water added to the second mixer is controlled by the density of the circulating absorption liquid, and its density ranges from 1.23 to 1.32. The pH value of the absorption liquid is controlled, and its pH range is 5.8-6.5, wherein the amount of alkali added to the first mixer is 90-95% of the total amount of alkali used, and the amount of alkali added to the second mixer is 5-5% of the total amount of alkali used 10%, the high-purity sodium sulfite unsaturated solution generated by the second regenerator is sent to the fine absorption section on the upper part of the absorption tower through the fine absorption pump, and the flue gas from the main absorption section is reabsorbed, so that the net flue gas discharged from the absorption tower is sulfur dioxide The content is reduced to below 40 mg/m ³ .

Compared with the existing sodium sulfite desulfurization technology, the present invention can greatly improve the desulfurization efficiency, is simpler and more reliable, has cheap and easy-to-obtain raw materials, is intrinsically safe, has no aerosol secondary pollution, has a higher desulfurization rate, and has a high concentration of effective components in the absorption liquid. The amount is small, the energy consumption of the circulation system is low, and the energy consumption of non-oxidizing air compression does not produce waste water. The process is simple and reliable, and the value-added range of by-products is greater than that of raw materials. Improve the existing sodium sulfite absorption desulfurization technology and apply it to flue gas desulfurization of coal-fired boilers and industrial kilns to achieve the emission standard of 40 mg/m ³ . On the one hand, it has the advantages of desulfurization rate and economy over calcium method and ammonia method.

Therefore, the two-step alkali-regeneration sodium sulfite method for removing sulfur dioxide from flue gas is relatively balanced in terms of investment, energy consumption, desulfurization rate, operating economy, and device reliability, and has a high promotion value. Widely used in thermal power plants, metallurgy, building materials, industrial kilns and chimneys.

Description of drawings

Fig. 1 is a structural schematic diagram of the present invention.

List of parts names in the figure:

1. Filter press, 2. Washing pump, 3. Chimney, 4. Absorption tower, 5. Washing tower, 6. Washing liquid tank, 7. First regenerator, 8. First mixer, 9. Main absorption pump , 10, feed pump, 11, thickener, 12, centrifuge, 13, mother liquor tank, 14, mother liquor pump, 15, second regenerator, 16, second mixer, 17, fine absorption pump, 18, Filter feed pump.

Detailed ways

Accompanying drawing 1 is embodiment of the present invention

The content of the invention is further described in conjunction with accompanying drawings and embodiments:

Example 1

With reference to shown in Fig. 1, a kind of two-step alkali regeneration sodium sulfite and sulfur dioxide removal device in the flue gas, the device consists of filter press, washing pump, chimney, absorption tower, washing tower, washing liquid tank, the first regenerator, Composed of the first mixer, main absorption pump, feed pump, thickener, centrifuge, mother liquor tank, mother liquor pump, second regenerator, second mixer, fine absorption pump and filter feed pump, the device includes two The two-stage countercurrent absorption unit and the two-step alkali regeneration unit for the absorption liquid, wherein, the two-stage countercurrent absorption unit consists of a chimney 3, an absorption tower 4, a washing tower 5, a washing liquid tank 6, a washing pump 2, a filter press 1, a main The absorption pump 9, the fine absorption pump 17 and the filter feed pump 18 are composed; the two-step alkali regeneration unit of the absorption liquid is composed of the first regenerator 7, the first mixer 8, the feeding pump 10, the thickener 11, the centrifuge machine 12, mother liquor tank 13, mother liquor pump 14, second regenerator 15 and second mixer 16; the flue gas pipeline from outside the device is connected with the flue gas inlet at the bottom of the washing tower 5, and the washing tower 5 is connected with the flue gas at its upper part The flue gas channels of the absorption tower 4 are connected, and the top outlet of the absorption tower 4 is connected with the chimney 3; the washing tower 5 is connected with the washing liquid tank 6 below it, and the inlet of the washing pump 2 is connected with the liquid outlet of the washing liquid tank 6 through a pipeline, and its outlet It is connected with the nozzle of the spray liquid of the washing tower 5 through a pipeline; the inlet of the filter feed pump 18 is connected with the mud outlet at the bottom of the washing liquid tank 6 through a valve, and the outlet of the filter feed pump 18 is connected with the liquid inlet of the filter press 1, and the filter press The outlet of machine 1 is connected to the side inlet of washing liquid tank 6; the inlet of main absorption pump 9 is connected to the outlet of the lower part of absorption tower 4, and its outlet is connected to the nozzle of the spray liquid on the side of the middle part of absorption tower 4; the fine absorption pump 17 The inlet of the second regenerator 15 is connected to the outlet, and the outlet of the fine absorption pump 17 is connected to the absorption liquid inlet on the upper side of the absorption tower 4 through pipes and valves; the liquid inlet of the first regenerator 7 is connected to the first mixer 8 is connected to the outlet, its liquid outlet is connected to the inlet of the material passing pump 10, the exhaust port on the top of the first regenerator 7 is connected to the top of the washing tower 5 through a pipeline, and the top inlet of the first mixer 8 is used for adding alkali The port is connected to the inlet pipe of the main absorption pump 9 through a pipeline; one side inlet of the thickener 11 is connected to the outlet of the feeding pump 10, the other side overflow port is connected to the inlet of the mother liquid tank 13, and the outlet at the bottom of the thickener 11 passes through Pipes and valves are connected to the centrifuge 12; the inlet of the mother liquor pump 14 is connected to the outlet of the mother liquor tank 13, and its outlet is connected to the side port of the second mixer 16 through a valve, and the top inlet of the second mixer 16 is used for adding alkali and tap water. Its bottom outlet is connected with the inlet of the second regenerator 15, and the outlet of the second regenerator 15 is connected with the inlet of the fine absorption pump 17.

Example 2

A kind of method for removing sulfur dioxide in the flue gas is carried out according to the following steps:

1) The flue gas containing sulfur dioxide and soot from outside the device enters the washing tower 5 and contacts with the spray washing liquid from the washing pump 2 to wash dust and cool down, and then enters the absorption tower 4 from the bottom at a temperature of 55-65°C to flow upwards, The internal space of the absorption tower 4 is in full contact with the circulating absorption liquid sent in by the main absorption pump 9 and the regenerated absorption liquid sent in by the fine absorption pump 17 in turn, and the sulfur dioxide in the flue gas reacts with the sodium sulfite in the recirculated absorption liquid and the regenerated absorption liquid Generate sodium bisulfite and be removed, and the net flue gas after removing sulfur dioxide enters the chimney 3 from the top of the absorption tower 4 to be emptied;

2) The washing liquid sprayed by the washing tower 5 is mainly water, which contains smoke and a small amount of soluble salts brought in by the flue gas. The soot is sprayed and washed, and then the washing liquid is returned to the washing liquid tank 6 by the washing tower 5, and the washed smoke and dust are settled and enriched at the bottom of the washing liquid tank 6, and are regularly sent to the filter press 1 through the filter feeding pump 18 for removal. The smoke and dust in the washing liquid, the separated clear liquid is returned to the washing tank 6 for recycling, and the dust sludge with a water content of 30-50% discharged from the filter press 1 is transported out to be mixed with the slag, and a small amount of soluble salts are brought out with the dust sludge, and washed The evaporated water is supplemented by tap water;

3) In the absorption tower 4, the flue gas and the absorption liquid undergo absorption reaction at 55°C to 65°C and a gauge pressure of 3kPa. The absorption liquid sprayed in the middle is a mixed solution of sodium sulfite and sodium bisulfite, which is fed by the main absorption pump 9 Conveyance cycle absorption, the absorption liquid will consume part of the sodium sulfite in the process of chemical reaction with the sulfur dioxide in the flue gas in each cycle, and generate more sodium bisulfite at the same time, the outlet of the absorption tower 4 is split to a part of the absorption liquid of the regeneration unit The sodium bisulfite taken away and the sodium sulfite brought back to the absorption tower after regeneration are used to maintain the stability of the composition of the circulating absorption liquid. The pH value of the circulating absorption liquid is in the range of 5.8-6.5, and the gas phase sulfur dioxide concentration in equilibrium with the liquid phase is 100-200 mg/m ³ ;

4) The absorption liquid used in the fine absorption section of the upper space of the absorption tower (4) is the regenerated absorption liquid returned by the regeneration unit, its composition is close to the pure sodium sulfite saturated solution, and only contains a very small amount of sodium bisulfite. The pH value is between 10.0- 10.8 range, the gaseous sulfur dioxide concentration in equilibrium with the liquid phase is 6-10 mg/m ³ ;

5) The fine absorption section on the upper part of the absorption tower (4) is a packing and tray structure. All the regenerated absorption liquid passes through the packing layer at one time and no longer circulates. The pH value of the absorption liquid flowing down from the packing layer is in the range of 9-10. The circulating absorption liquid in the middle part of the absorption tower 4 stabilizes the pH value of the circulating absorption liquid in the main absorption section in the range of 5.8-6.5;

6) By sending a part of the absorption liquid to the regeneration unit for regeneration by adding alkali to maintain the pH value of the circulating absorption liquid in the absorption tower (4) in the range of 5.8-6.5 to maintain its continuous desulfurization ability, the regeneration by adding alkali can With caustic soda or soda ash, a part of the circulating absorption liquid discharged from the liquid collection section at the lower part of the absorption tower 4 is split into the first regenerator 7 through the first mixer 8 for regeneration reaction. The amount of split depends on the amount of sulfur dioxide brought in by the flue gas. The regeneration reaction makes sodium bisulfite into sodium sulfite with less solubility, a part of sodium sulfite generates crystals in the first regenerator 7, more sodium sulfite dissolves in the mother liquor and enters the mother liquor tank 13 after being separated by the centrifuge 12, and the sodium sulfite crystals pass through the centrifuge 12. The separated crystals are discharged into the device as finished products, dried and packaged for storage, and the sodium sulfite crystals leave the solution system to maintain the material balance of the circulating absorption liquid;

7) There is a small amount of undecomposed sodium bisulfite in the mother liquor after the separation of sodium sulfite crystals, and the mother liquor is transported by the mother liquor pump 14 through the second mixer 16 and enters the second regenerator 15 for further regeneration reaction to convert all sodium bisulfite into sodium sulfite , the second regenerator 15 also adds metered tap water to keep the water balance of the absorption tower 4, that is, the water content of the circulating absorption liquid is in a controllable range, and solid crystallization does not occur in the absorption tower 4 during the absorption process. Sodium sulfite crystallization is produced in the reaction of regenerator 7;

8) The amount of water added to the washing tower 5 is controlled by the liquid level of the washing liquid tank 6, and the amount of water added to the second mixer 16 is controlled by the density of the circulating absorption liquid. The density range is 1.23-1.32. The total amount of alkali used is determined by the sulfur dioxide brought in by the flue gas , is controlled by the pH value of the circulating absorption liquid, and its pH range is 5.8-6.5, wherein the amount of alkali added to the first mixer 8 is 90-95% of the total amount of alkali used, and the amount of alkali added to the second mixer 16 is the total amount of alkali used. 5-10% of the amount of alkali, the high-purity sodium sulfite unsaturated solution generated by the second regenerator 15 is sent to the fine absorption section on the upper part of the absorption tower 4 through the fine absorption pump 17, and the flue gas from the main absorption section is absorbed again, so that The sulfur dioxide content of the net flue gas discharged from the absorption tower 4 is reduced to below 40 mg/m ³ .

The first step regeneration purpose of the present invention is to eliminate most of sodium bisulfite to obtain sodium sulfite crystals and then separate.

The purpose of the second step of regeneration is to eliminate all sodium bisulfite to obtain a pure sodium sulfite solution with stronger absorption capacity.

Different absorption units are used, and the absorption liquid is divided into two countercurrent absorptions to solve the following problems:

The main absorption section of the present invention still uses the mixed solution of sodium sulfite and sodium bisulfite to achieve the desulfurization rate index (≦400 mg/m ³ ) of the existing sodium sulfite desulfurization technology, and remove more than 90% of the total sulfur dioxide in the flue gas.

The fine absorption section uses the pure sodium sulfite solution with stronger absorption capacity obtained from the second-step regeneration unit, and continues to desulfurize the flue gas after desulfurization in the main absorption section, reducing the sulfur dioxide in the net flue gas to below 40 mg/m ³ .

Afterwards, the absorption liquid is added to the absorption liquid in the main absorption section by itself. The structure of the fine absorption section is similar to the foam trapping layer of the existing empty tower technology, without increasing the complexity of equipment and processes, and without changing the operating conditions of the main absorption section.

In summary

The sodium sulfite method, like the ammonia method, does not have a desulfurizer preparation system, no waste water is produced, and the process is simpler than the calcium method;

The effective absorption component of the absorption liquid of the sodium sulfite method is soluble salt. Compared with the calcium method and the ammonia method desulfurizer, its effective concentration is the highest, the absorption capacity is the strongest, and the allowable liquid-gas ratio is the smallest, which is beneficial to reduce the circulation of the absorption liquid and save power consumption. The sodium sulfite method is also the only one among the three methods that does not require forced blowing of air to oxidize the absorption liquid, which saves more power;

The biggest feature of the sodium sulfite method is that it is the only desulfurization technology that can use high-purity absorption liquid in the absorption tower for two-step fine absorption. This is essentially different from the calcium method to increase the spray volume and increase the absorption rate simply and repeatedly. However, the existing sodium sulfite method desulfurization technology The potential for high-purity absorption is not exploited.

The regeneration liquid returned to the absorption tower by the sodium sulfite method has a lower "gas phase sulfur dioxide equilibrium concentration" than the absorption liquid by the calcium method and ammonia method, which is the technical basis for achieving a higher desulfurization rate than the existing flue gas desulfurization technology. Making good use of this basic condition can achieve lower cost and higher desulfurization rate than calcium and ammonia desulfurization technologies.

Claims (2)

1. a step adds alkali regeneration Arbiso process and removes sulfur dioxide in flue gas device, this device is by filter press, washing pump, chimney, absorption tower, scrubbing tower, washing liquid bath, first regenerator, first blender, main absorption pump, punishment in advance pump, thickener, centrifuge, mother liquor tank, mother liquor pump, Second reactivator, second blender, essence absorption pump and filtration feed pump composition, it is characterized in that this device comprises two-stage countercurrent absorptive unit and absorbing liquid two step adds alkali regeneration unit, wherein, described two-stage countercurrent absorptive unit is by chimney (3), absorption tower (4), scrubbing tower (5), washing liquid bath (6), washing pump (2), filter press (1), main absorption pump (9), essence absorption pump (17) and filtration feed pump (18) composition, described absorbing liquid two step adds alkali regeneration unit and is made up of the first regenerator (7), the first blender (8), punishment in advance pump (10), thickener (11), centrifuge (12), mother liquor tank (13), mother liquor pump (14), Second reactivator (15) and the second blender (16), be connected from the gas approach of the flue outside device with scrubbing tower (5) bottom, scrubbing tower (5) communicates with the exhaust gases passes on the absorption tower (4) being located thereon portion, and absorption tower (4) top exit is connected with chimney (3), scrubbing tower (5) is connected with the washing liquid bath (6) below it, and the import of washing pump (2) is connected by the liquid outlet of pipeline with washing liquid bath (6), and its outlet is connected by the spray liquid mouth of pipe of pipeline with scrubbing tower (5), filter feed pump (18) import to be connected with washing liquid bath (6) bottom slurry outlet by valve, filter feed pump (18) outlet and be connected with filter press (1) inlet, filter press (1) leakage fluid dram is connected with washing liquid bath (6) side-entrance, the import of main absorption pump (9) is connected with absorption tower (4) bottom leakage fluid dram, and its outlet is connected with the spray liquid mouth of pipe of side, absorption tower (4) middle part, the import of essence absorption pump (17) exports with Second reactivator (15) and is connected, and the outlet of smart absorption pump (17) is connected with the absorbing liquid import of valve with absorption tower (4) upper side by pipeline, the inlet of described first regenerator (7) export with the first blender (8) be connected, its liquid outlet is connected with the import of punishment in advance pump (10), the exhaust outlet at the first regenerator (7) top is connected by pipeline with the top of scrubbing tower (5), and the top inlet of the first blender (8) is used for adding the import of alkali side and is connected by the inlet pipeline of pipeline with main absorption pump (9), the side import of described thickener (11) exports with punishment in advance pump (10) and is connected, and another side overfall is connected with mother liquor tank (13) import, and thickener (11) outlet at bottom is connected with centrifuge (12) with valve by pipeline, the import of described mother liquor pump (14) exports with mother liquor tank (13) and is connected, its outlet is connected with the second blender (16) side import by valve, second blender (16) top inlet is used for adding alkali and running water, second blender (16) outlet at bottom is connected with Second reactivator (15) import, Second reactivator (15) outlet is connected with the import of smart absorption pump (17).

2. adopt the method removing sulfur dioxide in flue gas of device described in claim 1, carry out in the steps below:

1), enter scrubbing tower (5) containing sulfur dioxide and the flue gas of flue dust outward from device to contact with the spray washing liquid from washing pump (2) and carry out giving a dinner of welcome and lowering the temperature, enter absorption tower (4) with the temperature of 55-65 DEG C from bottom afterwards upwards to flow, the regenerable absorbent liquid that the circulating absorption solution sent into main absorption pump (9) successively in absorption tower (4) inner space and smart absorption pump (17) are sent into fully contacts, sodium sulfite in sulfur dioxide in flue gas and circulating absorption solution and regenerable absorbent liquid reacts and generates sodium hydrogensulfite and be removed, neat stress after scrubbing CO_2 enters chimney (3) emptying by absorption tower (4) top,

2), scrubbing tower (5) spray cleaning solution based on water, the flue dust brought into containing flue gas and a small amount of soluble salts, deliver into scrubbing tower (5) by washing liquid bath (6) through washing pump (2) circulation and spray washing is carried out to the flue dust that flue gas carries, cleaning solution returns washing liquid bath (6) by scrubbing tower (5) afterwards, washing liquid bath (6) bottom is enriched in by the flue dust sedimentation under washing, the flue dust in cleaning solution is regularly removed via filtration feed pump (18) feeding filter press (1), isolated clear liquid returns sink (6) and recycles, the dirt mud outward transport of the moisture 30-50% that filter press (1) is discharged mixes with slag, a small amount of soluble salts is taken out of with dirt mud, cleaning solution is supplemented by running water by the water evaporated,

3), in absorption tower (4), flue gas and absorbing liquid are at 55 DEG C ~ 65 DEG C, absorption reaction is carried out under gauge pressure 3kPa condition, the absorbing liquid of middle part spray is the mixed solution of sodium sulfite and sodium hydrogensulfite, absorbed by main absorption pump (9) delivery cycle, absorbing liquid part sodium sulfite that all can consume wherein in each circulation with the process of the sulfur dioxide chemical reaction in flue gas generates more sodium hydrogensulfite, the sodium sulfite that absorption tower (4) outlet manifold goes a part of absorbing liquid of regeneration unit to take away and the sodium sulfite taking back absorption tower are stablized in order to the composition maintaining circulating absorption solution, circulating absorption solution pH value is in 5.8-6.5 scope, be 100-200 milligram/m with the gas phase sulfur dioxide concentration of this liquid equilibrium ³,

4) absorbing liquid, for absorption tower (4) upper space essence absorber portion is the regenerable absorbent liquid returned by regeneration unit, its composition is close to pure sodium sulfite saturated solution, only containing minute quantity sodium hydrogensulfite, its pH value, in 10.0-10.8 scope, is 6-10 milligram/m with the gas phase sulfur dioxide concentration of liquid equilibrium ³;

5), the smart absorber portion on absorption tower (4) top is filler and tray structure, whole regenerable absorbent liquid is disposable not to be recycled by packing layer, the absorbing liquid pH value flowed down by packing layer is in 9-10 scope, supplement the circulating absorption solution entering middle part, absorption tower (4), make main absorber portion circulating absorption solution pH value be stabilized in 5.8-6.5 scope;

6), carry out adding by a part of absorbing liquid being sent to regeneration unit circulating absorption solution pH value that mode that alkali regeneration returns to absorption tower maintains absorption tower (4) keeps holding its lasting desulfurization ability in 5.8-6.5 scope, described add alkali regeneration caustic soda or with soda ash, the circulating absorption solution that absorption tower (4) bottom liquid collecting section is discharged is shunted a part and is entered the first regenerator (7) through the first blender (8) and carry out regenerative response, the quantity of shunting depends on the sulfur dioxide quantity that flue gas is brought into, regenerative response makes sodium hydrogensulfite become the less sodium sulfite of solubility, part sodium sulfite generates crystallization at the first regenerator (7), more sodium sulfite is dissolved in mother liquor and enters mother liquor tank (13) after centrifuge (12) is separated, sodium sulfite crystal is the outer drying and packaging warehouse-in of finished product bleeder through centrifuge (12) isolated crystal, the sodium sulfite crystal of centrifugation leaves solution system makes the material of circulating absorption solution be balanced,

7), be separated in the mother liquor after sodium sulfite crystal and there is a small amount of undecomposed sodium hydrogensulfite, mother liquor enters the further regenerative response of Second reactivator (15) by mother liquor pump (14) conveying through the second blender (16) makes sodium hydrogensulfite all be converted into sodium sulfite, Second reactivator (15) also add through metering running water to keep the water balance of absorption tower (4), namely the water content of circulating absorption solution is at controlled range, in absorption process, absorption tower (4) inside does not occur that solid crystal can produce sodium sulfite crystallization again in the reaction of the first regenerator (7),

8), scrubbing tower (5) amount of water is by washing liquid bath (6) Liquid level, second blender (16) amount of water is by circulating absorption solution density domination, its density range 1.23-1.32, the sulfur dioxide that total alkali charge is brought into by flue gas determines, control by circulating absorption solution pH value, its pH value range 5.8-6.5, the alkali number wherein adding the first blender (8) is the 90-95% of total alkali charge, the alkali number adding the second blender (16) is the 5-10% of total alkali charge, the high-purity sodium sulfite unsaturated solution that Second reactivator (15) generates sends into the smart absorber portion on absorption tower (4) top through smart absorption pump (17), the flue gas carrying out autonomous absorber portion is absorbed again, the neat stress content of sulfur dioxide that absorption tower (4) is discharged is reduced to 40 milligrams/m ³below.